The present invention relates to mufflers, and more particularly, to high performance mufflers used to attenuate the sound waves in exhaust gases of internal combustion engines and the like (e.g., automotive vehicle engines, turbine engines, compressed gas power tools, etc.).
Exhaust gases from internal combustion engines and the like includes sound waves that many consider objectionable noise. Mufflers have been used for years in attempts to muffle or attenuate the sound waves by modifying and/or eliminating certain of the frequencies of the sound waves. A longstanding goal of those working in the muffler art has been to have the mufflers produce a pleasing sound or tone at an acceptable level.
In the past, various muffler designs or constructions have been proposed and/or used. One commonly used types of muffler design include baffled flow paths for the exhaust gases. Changes in the flow path direction of the exhaust gases, over short distances, caused by the baffles have effectively reduced the noise level. Nevertheless, these baffle-type mufflers have an undesirable side effect of tending to create high back pressure on the engines. Such back pressures reduce the power and efficiency of the engines.
Other muffler designs have directed the exhaust gases through perforated tubes that are surrounded by sound absorbing material, such as glass fibers, commonly known as "glass-pack" or "glass-wool". While these "glass pack" or "glass-wool" type mufflers generally produce lower back pressures on the engine, many find the resulting sound and the level of sound to be objectionable.
So-called "high performance" mufflers have been developed and are recognized by those in the muffler art to be a distinct type or class of muffler. High performance mufflers tend to be smaller or more compact in size than mufflers typically used with conventional automobiles. They usually create a low back pressure on the engine and a level of sound and a tone that are considered pleasing to persons who drive and appreciate high performance automobiles and that are not objectionable to others. Such a high performance muffler is disclosed in U.S. Pat. No. 5,033,581. The patented muffler includes at least two separate gas tubes or passages interconnected in series with a single or multiple tail pipe. At least one of the gas tubes has a length greater than that of the other or others. The total cross-sectional areas of all of the gas tubes are approximately equal to or greater than the cross-sectional area of the single or multiple exhaust manifold or the single or multiple tail pipes. In one embodiment, a housing encloses the gas tubes. In this embodiment, at least one of the gas tubes is perforated, and the space between the gas tubes and the housing is filled with a sound absorbing material.
There remains, however, a recognized need in the muffler art for an improved high performance muffler that can be used with both high performance and conventional automobiles, that will enhance the engine's power and efficiency and that will produce a level of sound and a tone that most will agree is pleasant and acceptable.